1. Field of the Invention
The present invention relates to a micrometer for measuring dimension of a workpiece such as length and thickness.
2. Description of Related Art
In FIG. 3, a conventional micrometer 100 (first conventional art) has an approximately U-shaped frame 101, an anvil 102 held at one end of the frame 101, a spindle 104 screwed to the other end of the frame 101 through a retainer sleeve 103 and moved toward and away from the anvil 102, a thimble 105 secured to the spindle 104 and fitted to an outer circumference of the retainer sleeve 103, and a ratchet mechanism 106 provided to a rear end of the spindle 104 for idly spinning when a more than predetermined load is applied to the spindle 104.
Though not shown, the ratchet mechanism 106 has a pair of ratchet wheels meshing with each other and a compression helical spring for biasing the ratchet wheels in a direction to mesh each other, the ratchet wheels spinning idly when a more than predetermined load is applied to the spindle 104.
During measurement, the frame 101 is held by left hand and the thimble 105 is rotated by right hand to sandwich a workpiece between the anvil 102 and the spindle 104. When the ratchet mechanism 106 is operated (rotated) by right hand while sandwiching the workpiece, the ratchet wheel idly spins with the more than predetermined load being applied to the spindle 104, so that the spindle 104 stops rotating, thus keeping constant measuring pressure.
Another example of micrometer is shown in Japanese Patent Laid-Open Publication No. Hei 7-103749 (second conventional art).
Similarly to the micrometer 100 of the above-described first conventional art, the micrometer according to the second conventional art has a frame, an anvil, a retainer sleeve, a spindle and a thimble. A constant-force device provided to the micrometer has a plate spring provided on an outer circumference of rear end of the retainer sleeve, and a ratchet wheel in contact with a proximal end of the plate spring and provided to an inner circumference of the thimble. The constant-force device allows the thimble to spin idly by elastic deformation of the plate spring when a more than predetermined load is applied between the thimble and the retainer sleeve.
During measurement, the thimble is rotated while holding the frame with one hand. When the thimble is further rotated during the above condition to apply more than predetermined load the spindle (between the thimble and the retainer sleeve), the thimble spins idly, thus keeping constant measuring pressure of the spindle during measurement.
The micrometer according to the above first conventional art is mainly used for measurement with both hands and the micrometer of the above second conventional art is mainly used for measurement with single-handed. No single micrometer can be used for both of single-handed operation and double-handed operation.
In this case, the constant-force device of the first conventional art and the second conventional art may be installed in a single micrometer for both the single-handed operation and the double-handed operation. However, according to the above arrangement, since the constant-force device of the first conventional art functions during single-handed operation and the constant-force device of the second conventional art functions during double-handed operation, the measuring pressure may differ according to type of operation, thus increasing measurement error.
Further, since the micrometer of the first conventional art and the second conventional art requires separate component according to the type of the constant-force device, the number of required components increases. Further, when both of the constant-force devices are installed in a single micrometer, the number of required components for one micrometer is increased, so that production cost is increased and measurement error may be likely to occur.
An object of the present invention is to provide a micrometer capable of measuring by both of single-handed operation and double-handed operation and capable of obtaining identical operability during single-handed operation and double-handed operation during respective measurement, thus reducing required number of components and eliminating measurement error according to type of operation.
A micrometer according to the present invention has: an approximately U-shaped frame; an anvil held on one end of the frame; a spindle screwed to the other end of the frame through a retainer sleeve and movable toward and away from the anvil; a thimble secured to the spindle and fitted to an outer circumference of the retainer sleeve. The micrometer is characterized in having: an operation sleeve rotatable relative to the spindle, the operating sleeve integrally having, on an outer side of an end remote from the end opposing the anvil, a first operation section with a smaller diameter than the diameter of the retainer sleeve and a second operation section fitted to an outer circumference of the thimble; and a constant-force device provided on either between the first operation section of the operation sleeve and the outer end of the spindle or between the second operation section of the operation sleeve and the outer circumference of the thimble, the constant-force device idly spinning when a more than predetermined load is applied to the spindle.
In the present invention, the thimble and the spindle are rotated through either the first constant-force device or the second constant-force device by rotating the operation sleeve integrally having the first operation section and the second operation section.
During measurement, the operation sleeve is rotated while disposing a workpiece between the anvil and the spindle, thus sandwiching the workpiece between the anvil and the spindle. The operation sleeve is further rotated under the above condition, so that either the first constant-force device or the second constant-force device is actuated when a more than predetermined load is applied to the spindle, thus idly spinning the operation sleeve. Since the operation sleeve integrally has the first operation section and the second operation section, the operation sleeve is rotated in a predetermined direction by either the double-handed operation for holding the frame by left hand and rotating the first operation section by right hand or by single-handed operation for holding the frame and rotating the second operation section with a single-handed. Further, during both operations, the same operability as in the conventional operation can be obtained.
Since the arrangement of the frame, anvil, retainer sleeve, spindle, thimble and operation sleeve can be commonly used both in providing the first constant-force device to the first accommodation space and second constant-force device to the second accommodation space, the number of components can be reduced.
Since only one constant-force device is installed in the micrometer, there is not measurement error between measurement by the single-handed operation and the double-handed operation.
In the present invention, a first accommodation space and a second accommodation space for accommodating the constant-force device may preferably formed respectively between the first operation section of the operation sleeve and the outer end of the spindle and between the second operation section of the operation sleeve and the outer circumference of the thimble.
According to the above arrangement, since the first accommodation space and the second accommodation space for accommodating the constant-force devices are formed to the micrometer, one of the constant-force devices can be installed to one of the accommodation spaces, thus easily constructing the micrometer having either the first constant-force device or the second constant-force device. Further, the constant-force device can be selected from a plurality of devices, and the constant-force device can be easily exchanged.
In the present invention, the first constant-force device accommodated in the first accommodation space may preferably include: a first ratchet wheel fixed to an inner circumference of the first operation section; a second ratchet wheel meshing with the first ratchet wheel and unrotatable and displaceable relative to the spindle in an axis direction; and a compression coil spring for biasing the second ratchet wheel toward the first ratchet wheel, the second constant-force device accommodated in the second accommodation space having an elastic member with one end being engaged to either one of the outer circumference of the thimble and the inner circumference of the second operation section and the other end being in contact with the other one of the outer circumference of the thimble and the inner circumference of the second operation section.
According to the above arrangement, since the first constant-force device and the second constant-force device employing known technique can be selectively installed to the micrometer, the micrometer capable of both the single-handed operation and the double-handed operation can be easily constructed. Further, the same touch (such as sound and operation feeling) as in the conventional ratchet constant-force device can be obtained in the first constant-force device and the same touch as so-called friction constant-force device using spring can be obtained in the second constant-force device.
In the present invention, a section of the thimble fitted to the second operation section may preferably be thinner than a section of the thimble not fitted to the second operation section.
According to the above arrangement, since the section fitted to the second operation section of the thimble is thinner than the section not fitted to the second operation section, the diameter of the second operation section can be reduced, thus retaining operability and size of a conventional micrometer.